Simple High-Spin Index L _ij for Ferromagnetic Organic Molecules

Abstract

The assessment of the high-spin stability of a molecule using indices, rules, etc. plays an important role in the design of ferromagnetic materials. In this chapter, we propose a simple high-spin stability index L _ij , which is related to the exchange integral K _ij , using computational and analytical approaches. The computational approach requires only non-bonding molecular orbital coefficients and subsequent unitary rotations to calculate the index $L_{ij}^{\hbox{min} }$. On the other hand, the analytical approach can predict the index $L_{ij}^{\hbox{min} }$ for larger systems without requiring direct quantum chemistry calculations. Using a variety of examples, we examine the reliability of the index by comparing the results with the high-spin stability ∆E(L − H) obtained from ab initio calculations including electron correlation effects. We also note that L _ij provides us with an efficient strategy for designing high-spin systems while considering the correlation effects.